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A hydrate with a 2:1 molecular ratio of anhydrous compound to water, plaster of paris is the hemihydrate of calcium sulfate, composition CaSO4·½H2O.
A hydrate which contains one-half molecule of water to one molecule of the compound; the most common such material is partially dehydrated gypsum (plaster of paris).
References in periodicals archive
The complete dissolution of hemihydrate
into dehydrate as the plaster were set form series of interlocking of dehydrate crystal matrix (capillaries) giving the plaster the ability to absorb water after it's dry.
Due to the hemihydrate
is an intermediate phase between the dihydrate and the anhydrous, which is metastable at all temperatures, in standard analyses of the Ca-S[O.sub.4]-[H.sub.2]O system only the dihydrate and the anhydrous phases are considered.
In chemical terms the codeine is 7,8-didehydro-4,5alpha-epoxy-3-methoxy-17- methylmorphinan-6-alpha-olphosphate (1:1) (salt) hemihydrates
(Fig: 3) .